It's a rule I have. Every place I spend time should be better because I was there.
Everywhere. A table at Starbucks? I'll wipe it off with a napkin when I sit down, and pick up my mess when I leave.
Be friendly to staff everywhere. Tip great service well. Point out terrible service politely to a manager, because terrible service is bad for everyone (the server, manager, business, and customers are all worse off if terrible service is happening).
Lightly clean any room you go to.
Don't trash a room just because other people are going to clean it.
In really messy, gross environments you're going to be only for a short time, at least don't make it worse.
If you see any hazards on a sidewalk or road that could hurt someone, move them.
In a space that's your own space, spend five minutes per day cleaning it one little area of it. Run a dustcloth or wet paper towel or napkin over one small corner of the room or area.
Maintain your clothing, tools, furnishings, and everything else around you.
If you're living on the road, your bag is your home. Occasionally lightly clean the inside of your pack or suitcase, mend any damage you can fix, throw out junk you've accumulated.
If you're someone's guest, buy/cook more food, groceries, and toiletries, or give them a nice and practical gift, or both.
Wash the dishes if you stay with someone and they've got dishes.
If every space your enter is better after you were there, you become welcome in many more spaces. It's good for your mind. It makes you feel welcome to walk into any area, knowing you're a force for good and you take care of your environment. It gets you into good habits so you treat your own important spaces well. It makes the world a better place.
Constantly improve your environment. Your life will be better if you do.
OK, So I'm only a year behind :)
I too like the idea of returning a borrowed item in better shape than you got it. I'll have to keep that in mind. I don't borrow much, but do sometimes.
I always make a point of holding the door for the next person coming along. It often surprises them, and of course there are the people who literally walk in while chatting on their phones and don't even acknowledge the service. So far I've avoided the urge to just let the door go on such people. But most people, even if they were off in their own world, will crack a smile and surface for a little while.
As for the original post - good suggestions. I always do some of that, but perhaps I'll give a little more thought to it now.
This reminds me of something my dad always told me:
"When you borrow something, return it in better condition as when you recieved it."
The impact of such little things can be amazing. Be nice to someone, e.g. hold open the door, and he'll maybe do the same to the next two people behind him. These two people will go on and hold the door open for the next two people behind them and so on. This doesn't have something to do with the environment directly but it surely has an impact on it.